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<p>In a <span class="t-spar">member-specification</span> of a <a href="class.html" title="cpp/language/class">class/struct</a> or <a href="union.html" title="cpp/language/union">union</a>, define the visibility of subsequent members.
</p>
<p>In a <span class="t-spar">base-clause</span> of a <a href="derived_class.html" title="cpp/language/derived class">derived class</a> declaration, define the accessibility of inherited members of the subsequent <span class="t-spar">base-specifier</span>s.
</p>
<table id="toc" class="toc"><tr><td>
<div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="access.html#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="access.html#Explanation"><span class="tocnumber">2</span> <span class="toctext">Explanation</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="access.html#In_detail"><span class="tocnumber">3</span> <span class="toctext">In detail</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="access.html#Public_member_access"><span class="tocnumber">4</span> <span class="toctext">Public member access</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="access.html#Protected_member_access"><span class="tocnumber">5</span> <span class="toctext">Protected member access</span></a></li>
<li class="toclevel-1 tocsection-6"><a href="access.html#Private_member_access"><span class="tocnumber">6</span> <span class="toctext">Private member access</span></a></li>
<li class="toclevel-1 tocsection-7"><a href="access.html#Inheritance"><span class="tocnumber">7</span> <span class="toctext">Inheritance</span></a></li>
</ul>
</td></tr></table>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span>
</h3>
<table class="t-sdsc-begin">

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<tr class="t-sdsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">public</span></span></span>  <code><b>:</b></code> <span class="t-spar">member-declarations</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td>
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</td>
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<tr class="t-sdsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">protected</span></span></span> <code><b>:</b></code> <span class="t-spar">member-declarations</span>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td>
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<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">private</span></span></span> <code><b>:</b></code> <span class="t-spar">member-declarations</span>
</td>
<td> (3)
</td>
<td class="t-sdsc-nopad">
</td>
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<tr class="t-sdsc">
<td> <span class="t-spar">class_name</span> <code><b>:</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">public</span></span></span> <span class="t-spar">base_classes</span>
</td>
<td> (4)
</td>
<td class="t-sdsc-nopad">
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<tr class="t-sdsc">
<td> <span class="t-spar">class_name</span> <code><b>:</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">protected</span></span></span> <span class="t-spar">base_classes</span>
</td>
<td> (5)
</td>
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<tr class="t-sdsc">
<td> <span class="t-spar">class_name</span> <code><b>:</b></code> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">private</span></span></span> <span class="t-spar">base_classes</span>
</td>
<td> (6)
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<div class="t-li1">
<span class="t-li">1)</span> The members declared after the specifier have public member access</div>
<div class="t-li1">
<span class="t-li">2)</span> The members declared declared after the specifier have protected member access</div>
<div class="t-li1">
<span class="t-li">3)</span> The members declared after the specifier have private member access</div>
<div class="t-li1">
<span class="t-li">4)</span> Public inheritance: the members of the <a href="derived_class.html" title="cpp/language/derived class">base classes</a> listed after the specifier keep their member access in the derived class</div>
<div class="t-li1">
<span class="t-li">5)</span> Protected inheritance: the public of the <a href="derived_class.html" title="cpp/language/derived class">base classes</a> listed after the specifier are protected members of the derived class</div>
<div class="t-li1">
<span class="t-li">6)</span> Private inheritance: the public and protected members of the <a href="derived_class.html" title="cpp/language/derived class">base classes</a> listed after the specifier are private members of the derived class</div>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span>
</h3>
<p>The name of every <a href="class.html" title="cpp/language/class">class</a> member (static, non-static, function, type, etc) has an associated "member access". When a name of the member is used anywhere a program, its access is checked, and if it does not satisfy the access rules, the program does not compile:
</p>
<div class="t-example">
<div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="kw1">class</span> Example <span class="br0">{</span>
 <span class="kw1">public</span><span class="sy4">:</span> <span class="co1">// all declarations after this point are public</span>
    <span class="kw4">void</span> add<span class="br0">(</span><span class="kw4">int</span> x<span class="br0">)</span> <span class="br0">{</span> <span class="co1">// member "add" has public access</span>
        n <span class="sy2">+</span><span class="sy1">=</span> x<span class="sy4">;</span> <span class="co1">// OK: private Example::n can be accessed from Example::add</span>
    <span class="br0">}</span>
 <span class="kw1">private</span><span class="sy4">:</span> <span class="co1">// all declarations after this point are private</span>
    <span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// member "n" has private access</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    Example e<span class="sy4">;</span>
    e.<span class="me1">add</span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK: public Example::add can be accessed from main</span>
<span class="co1">//  e.n = 7;  // Error: private Example::n cannot be accessed from main</span>
<span class="br0">}</span></pre></div></div>
<p><br> 
</p>
</div>
<p>Access specifiers give the author of the class the ability to decide which class members are accessible to the users of the class (that is, the <i>interface</i>) and which members are for internal use of the class (the <i>implementation</i>)
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: In detail">edit</a>]</span> <span class="mw-headline" id="In_detail">In detail</span>
</h3>
<p>All members of a class (bodies of <a href="member_functions.html" title="cpp/language/member functions">member functions</a>, initializers of member objects, and the entire <a href="nested_classes.html" title="cpp/language/nested types">nested class definitions</a>) have access to all the names to which a class can access. A local class within a member function has access to all the names the member function itself can access. 
</p>
<p>A class defined with the keyword <code>class</code> has private access for its members and its base classes by default. A class defined with the keyword <code>struct</code> has public access for its members and its base classes by default. A <a href="union.html" title="cpp/language/union">union</a> has public access for its members by default.
</p>
<p>To grant access to additional functions or classes to protected or private members, a <a href="friend.html" title="cpp/language/friend">friendship declaration</a> may be used.
</p>
<p>Accessibility applies to all names with no regard to their origin, so a name introduced by a <a href="typedef.html" title="cpp/language/typedef">typedef</a> or <a href="using_declaration.html" title="cpp/language/using declaration">using declarations</a> is checked, not the name it refers to.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> A <span class="sy4">:</span> X <span class="br0">{</span>
  <span class="kw1">class</span> B <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// B is private in A</span>
<span class="kw1">public</span><span class="sy4">:</span>
  <span class="kw1">typedef</span> B BB<span class="sy4">;</span> <span class="co1">// BB is public</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
  A<span class="sy4">::</span><span class="me2">B</span> y<span class="sy4">;</span> <span class="co1">// error, A::B is private</span>
  A<span class="sy4">::</span><span class="me2">BB</span> x<span class="sy4">;</span> <span class="co1">// OK, A::BB is public</span>
<span class="br0">}</span></pre></div></div>
<p>Member access does not affect visibility: names of private and privately-inherited members are visible and considered by overload resolution, implicit conversions to inaccessible base classes are still considered, etc. Member access check is the last step after any given language construct is interpreted. The intent of this rule is that replacing any <code>private</code> with <code>public</code> never alters the behavior of the program.
</p>
<p>Access checking for the names used in <a href="default_arguments.html" title="cpp/language/default arguments">default function arguments</a> as well as in the default <a href="template_parameters.html#Default_template_arguments" title="cpp/language/template parameters">template parameters</a> is performed at the point of declaration, not at the point of use.
</p>
<p>Access rules for the names of <a href="virtual.html" title="cpp/language/virtual">virtual functions</a> are checked at the call point using the type of the expression used to denote the object for which the member function is called. The access of the final overrider is ignored.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> B <span class="br0">{</span> <span class="kw1">virtual</span> <span class="kw4">int</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// f is public in B</span>
<span class="kw1">class</span> D <span class="sy4">:</span> <span class="kw1">public</span> B <span class="br0">{</span> <span class="kw1">private</span><span class="sy4">:</span> <span class="kw4">int</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// f is private in D</span>
<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
 D d<span class="sy4">;</span>
 B<span class="sy3">&amp;</span> b <span class="sy1">=</span> d<span class="sy4">;</span>
 b.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK: B::f() is public, D::f() is invoked even though it's private</span>
 d.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// error: D::f() is private</span>
<span class="br0">}</span></pre></div></div>
<p>A name that is private according to unqualified <a href="lookup.html" title="cpp/language/lookup">name lookup</a>, may be accessible through qualified name lookup:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> A <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> B <span class="sy4">:</span> <span class="kw1">private</span> A <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> C <span class="sy4">:</span> <span class="kw1">public</span> B <span class="br0">{</span>
   A<span class="sy2">*</span> p<span class="sy4">;</span> <span class="co1">// error: unqualified name lookup finds A as the private base of B</span>
   <span class="sy4">::</span><span class="me2">A</span><span class="sy2">*</span> q<span class="sy4">;</span> <span class="co1">// OK, qualified name lookup finds the namespace-level declaration</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>A name that is accessible through multiple paths in the inheritance graph has the access of the path with the most access:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> W <span class="br0">{</span> <span class="kw1">public</span><span class="sy4">:</span> <span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> A <span class="sy4">:</span> <span class="kw1">private</span> <span class="kw1">virtual</span> W <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> B <span class="sy4">:</span> <span class="kw1">public</span> <span class="kw1">virtual</span> W <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> C <span class="sy4">:</span> <span class="kw1">public</span> A, <span class="kw1">public</span> B <span class="br0">{</span>
<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> W<span class="sy4">::</span><span class="me2">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// OK, W is accessible to C through B</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>Any number of access specifiers may appear within a class, in any order. Member access specifiers may affect class layout: the addresses of non-static <a href="data_members.html#Layout" title="cpp/language/data members">data members</a> are only guaranteed to increase in order of declaration for the members with the same access. For <a href="../concept/StandardLayoutType.html" title="cpp/concept/StandardLayoutType"><code>StandardLayoutType</code></a>, all non-static data members must have the same access.
</p>
<p>When a member is redeclared within the same class, it must do so under the same member access:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> S <span class="br0">{</span>
  <span class="kw1">class</span> A<span class="sy4">;</span> <span class="co1">// S::A is public</span>
<span class="kw1">private</span><span class="sy4">:</span>
  <span class="kw1">class</span> A <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// error: cannot change access</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Public member access">edit</a>]</span> <span class="mw-headline" id="Public_member_access">Public member access</span>
</h3>
<p>Public members form a part of the public interface of the class (other parts of the public interface are the non-member functions found by <a href="adl.html" title="cpp/language/adl">ADL</a>).
</p>
<p>A public member of a class is accessible everywhere.
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> S <span class="br0">{</span>
 <span class="kw1">public</span><span class="sy4">:</span> <span class="co1">// n, f, E, A, B, C, U are public members</span>
    <span class="kw4">int</span> n<span class="sy4">;</span>
    <span class="kw4">static</span> <span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
    <span class="kw2">enum</span> E <span class="br0">{</span>A, B, C<span class="br0">}</span><span class="sy4">;</span>
    <span class="kw1">struct</span> U <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    S<span class="sy4">::</span><span class="me2">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// S::f is accessible in main</span>
    S s<span class="sy4">;</span>
    s.<span class="me1">n</span> <span class="sy1">=</span> S<span class="sy4">::</span><span class="me2">B</span><span class="sy4">;</span> <span class="co1">// S::n and S::B are accesisble in main</span>
    S<span class="sy4">::</span><span class="me2">U</span> x<span class="sy4">;</span> <span class="co1">// S::U is accessible in main</span>
<span class="br0">}</span></pre></div></div>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Protected member access">edit</a>]</span> <span class="mw-headline" id="Protected_member_access">Protected member access</span>
</h3>
<p>Protected members form the interface for the derived classes (which is distinct from the public interface of the class).
</p>
<p>A protected member of a class <code>Base</code> can only be accessed
</p>
<div class="t-li1">
<span class="t-li">1)</span> by the members and friends of <code>Base</code> </div>
<div class="t-li1">
<span class="t-li">2)</span> by the members <span class="t-rev-inl t-until-cxx17"><span>and friends</span> <span><span class="t-mark-rev t-until-cxx17">(until C++17)</span></span></span> of any class derived from <code>Base</code>, but only when operating on an object of a type that is derived from <code>Base</code> (including <code>this</code>)</div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> Base <span class="br0">{</span>
 <span class="kw1">protected</span><span class="sy4">:</span>
    <span class="kw4">int</span> i<span class="sy4">;</span>
 <span class="kw1">private</span><span class="sy4">:</span>
    <span class="kw4">void</span> g<span class="br0">(</span>Base<span class="sy3">&amp;</span> b, <span class="kw1">struct</span> Derived<span class="sy3">&amp;</span> d<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> Derived <span class="sy4">:</span> Base <span class="br0">{</span>
    <span class="kw4">void</span> f<span class="br0">(</span>Base<span class="sy3">&amp;</span> b, Derived<span class="sy3">&amp;</span> d<span class="br0">)</span> <span class="co1">// member function of a derived class</span>
    <span class="br0">{</span>
        <span class="sy2">++</span>d.<span class="me1">i</span><span class="sy4">;</span> <span class="co1">// okay: the type of d is Derived</span>
        <span class="sy2">++</span>i<span class="sy4">;</span> <span class="co1">// okay: the type of the implied '*this' is Derived</span>
<span class="co1">//      ++b.i; // error: can't access a protected member through Base</span>
    <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw4">void</span> Base<span class="sy4">::</span><span class="me2">g</span><span class="br0">(</span>Base<span class="sy3">&amp;</span> b, Derived<span class="sy3">&amp;</span> d<span class="br0">)</span> <span class="co1">// member function of Base</span>
<span class="br0">{</span>
    <span class="sy2">++</span>i<span class="sy4">;</span> <span class="co1">// okay</span>
    <span class="sy2">++</span>b.<span class="me1">i</span><span class="sy4">;</span> <span class="co1">// okay</span>
    <span class="sy2">++</span>d.<span class="me1">i</span><span class="sy4">;</span> <span class="co1">// okay</span>
<span class="br0">}</span>
 
<span class="kw4">void</span> x<span class="br0">(</span>Base<span class="sy3">&amp;</span> b, Derived<span class="sy3">&amp;</span> d<span class="br0">)</span> <span class="co1">// non-member non-friend</span>
<span class="br0">{</span>
<span class="co1">//    ++b.i; // error: no access from non-member</span>
<span class="co1">//    ++d.i; // error: no access from non-member</span>
<span class="br0">}</span></pre></div></div>
<p>When a pointer to a protected member is formed, it must use a derived class in its declaration:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> Base <span class="br0">{</span>
 <span class="kw1">protected</span><span class="sy4">:</span>
    <span class="kw4">int</span> i<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> Derived <span class="sy4">:</span> Base <span class="br0">{</span>
    <span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span>
    <span class="br0">{</span>
<span class="co1">//      int Base::* ptr = &amp;Base::i;    // error: must name using Derived</span>
        <span class="kw4">int</span> Base<span class="sy4">::</span><span class="sy2">*</span> ptr <span class="sy1">=</span> <span class="sy3">&amp;</span>Derived<span class="sy4">::</span><span class="me2">i</span><span class="sy4">;</span> <span class="co1">// okay</span>
    <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Private member access">edit</a>]</span> <span class="mw-headline" id="Private_member_access">Private member access</span>
</h3>
<p>Private members form the implementation of a class, as well as the private interface for the other members of the class.
</p>
<p>A private member of a class can only be accessed by the members and friends of that class, regardless of whether the members are on the same or different instances:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> S <span class="br0">{</span>
 <span class="kw1">private</span><span class="sy4">:</span>
    <span class="kw4">int</span> n<span class="sy4">;</span> <span class="co1">// S::n is private</span>
 <span class="kw1">public</span><span class="sy4">:</span>
    S<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> n<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">// this-&gt;n is accessible in S::S</span>
    S<span class="br0">(</span><span class="kw4">const</span> S<span class="sy3">&amp;</span> other<span class="br0">)</span> <span class="sy4">:</span> n<span class="br0">(</span>other.<span class="me1">n</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">// other.n is accessible in S::S</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>The <a href="explicit_cast.html" title="cpp/language/explicit cast">explicit cast</a> (C-style and function-style) allows casting from a derived lvalue to reference to its private base, or from a pointer to derived to a pointer to its private base.
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Inheritance">edit</a>]</span> <span class="mw-headline" id="Inheritance">Inheritance</span>
</h3>
<p>See <a href="derived_class.html" title="cpp/language/derived class">derived classes</a> for the meaning of public, protected, and private inheritance.
</p>
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